Electrical apparatus



Feb. 25, 1936. c l, MCNEIL ELECTRICAL APPARATUS Filed Jan. 51," 1954INVENTOR. C/mr/es Mc/Vefl BY ORNE.

I Pdtented Feb. 25, 1936 UNITED STATES PATENT OFFICE Eclipse AviationCorporation,

East Orange,

N. J., a corporation of New Jersey ApplicationJanuary 31, 1934, SerialNo. 709,210

3 Claims.

This invention relates to electric current generating and batterycharging systems such as are employed on motor vehicles, andparticularly to certain improvements to be associated 5 with the reversecurrent cut-outcommonly employed in such systems to open thebattery-generator circuit and prevent the discharging of the batterywhen the voltage of the generator becomes less than that of the battery.

1 In conventional compound generators the characteristics are frequentlysuch that a reverse current of insumcient value to cause an immediateopening oi the contacts of the reverse current cut-out may at the sametime be sufliciently 15' strong to produce a reversal of polarity in thegenerator itself, due to the'relationship or relative strengths of, theseries and shunt fields of the generator. That is, when the reversal ofcurrent occurs, such reversal produces a buck- 2 ing effect in theseries field of the generator,

which bucking effect reduces the effective voltage across the terminalsof the shunt field to such an extent that the polarity of the machinemay be reversed before the reverse current cutout function. Morespecifically, an object of the invention is to provide means formaintaining the shunt field of the generator comparatively free of theinfluence of such series field bucking tendency, whereby the strength ofthe shunt field may be held at a sufficient value to prevent reversal ofthe polarity of the generator.

A feature of the invention, therefore, is the provision of a systemhaving two safeguards 35 against reverse current tendencies, instead ofthe usual single safeguard; the first safeguard functioning during theinitial stage of current reversal, and continuing to function until theusual safe- 'guard-the opening of theconventional cut-out' 40 has hadsumcient time to become effective.\

In the embodiment of the invention herein illustrated and described, theshunt field controlling means operates to establish an alternate patafter the initial excitation, or building up 45 of he generator hastaken place. By reason of this alternate path, any reversal of currentwhich would ordinarily be sufficiently strong to create a danger ofreversal inpolarity in the generator, will have no efiect upon thestrength of the shunt 50 field, which will be energized at full batteryvoltage, and danger of reversal, thereby nullified;

It is to be understood however, that the method and means employed forthis purpose in the preierred embodiment as shown are merely illus- 55trative and do not define the limits of the invention, reference beinghad for the latter purpose to the appended claims In the drawing, thesingle figure is a diagrammatic representation of the electricalcircuits and parts involved in the preferred embodiment of theinvention, ,such parts including the generator armature 5 with the usualshunt and series windings 8 and 1 respectively, the former being inseries with a variable resistance 8 and in shunt across the out-putfeeds 9 and III. 'Feed 9 preferably includes the usual series winding llof the reverse current relay and the usual shunt or voltage winding l2,the former being connected with the battery through the normally closedarmature switch [4 and the latter having connection with the second feedI0 through the instrumentality of the lead I5.

The battery adapted to be charged by the generator is indicated at Itwith one terminal connected to feed I0 by way of lead H and its otherterminal to the second section 9a of the line 9 by way oi lead IS. Thelighting or other power consuming load l9 adapted to be supplied by thegenerator and/or battery is supplied by the ex-., tensions of lines Soand I0 indicated at 20 and 2|.

The novel means of the present invention for maintaining full strengthin the shunt field 6 even on those occasions when there is a reversal inthe direction 01' current flow in the windings of the reverse currentdevice, takes the form of a second relay including a winding 25connected across the main lines 9 and ID as indicated at 28 and 21 andhaving associated therewith an armature 28 movable into contact witheither of two conducting plates 29 and 30, the former being inconnection with main feed 9 and the latter being inconnection with thesecond section of the feed 90. through the provision of a connectinglead 32, suitable means such as the tension spring 33 being provided tomaintain the 40 said armature 28 in the upper position during startingof the generator, the setting of the spring and the design of the coil25 being preferably such that the electro-magnetic fieldproduced by theflow of current through said coil is insufficient to draw the armature28 downwar so into contact with the plate 30 during the starting orbuilding up period of the generator but becomes sumcient to produce suchdownward movement at the completion of the building up 0 period. -Or inother words, when the voltage across the lines 9 and I0 (and hence thevoltage across the coil l2 oi the reverse current cut-out) becomessufiicient to insure closing of the switch I4. When both these switchmovementsthat is, of the armatures 28 and ll-occur, the excitation ofthe shunt field will thereafter proceed through the conductors 9, ll,I4, 32, 30, 28 and 36 and will continue in this manner during the entireperiod of operation of the generator, ex-

- cept on occasions when there is a tendency for a reversal in thedirection of current fiow--that is, a tendency for the current to flowfrom the battery into the generator. The operation on such occasionswill be as follows: 7

As the current begins to flow in a reversed direction through the serieswinding M oi. the reverse current cut-out, there is of course a certaintime lag in the opening of the switch 5,,

during which time the above described bucking efiect will occur in theseries field winding 7. The shunt field winding, however, will bemaintained at full strength by reason of the direct connection with thebattery constituted by the lead 32 and including the contact 30 withwhich the armature 28 is engaged. This battery excitation through thisdirect path between the battery and the shunt field 5 will continue toconstitute the means for maintaining the shunt field at full batterystrength until after actual opening of the switch M. When such openingoccurs, the above described bucking efiect ceases and there is then nofurther necessity of main taining full strength of current flow in theshunt field.

So long as the voltage across the generator terminals remains at orabove the predetermined value, the coil 25 holds the strength of themagnetic field acting upon the armature 28 at such a value that thespring 33 is unable to return the armature 28 to a position ofengagement with the contact plate 29, and such return .will be delayeduntil just prior to the return of the generator rotor to a condition ofrest, at which time the return of the armature 28 to contact withconductor 29 will serve to place the parts in condition forself-excitation of the generator on the occasion of the next startingthereof, on which occasion the cycle of operation above described willof course be repeated.

There is thus disclosed a system in which the reversal effects of theoperating current of reverse current cut-out devices are nullified bymaintaining the shunt field excitation at a value equivalent tooperating conditions until after complete opening of the reverse currentrelay or cut-out and the effect of the reverse current has expired.

What is claimed is:

1. In a system of the class described, a battery and generator connectedfor energization of the 5 former upon rotation of the latter, a reversecurrent cut-out between the generator and battery, a shunt fieldconstituting part of the generator, means for energizing said field bycurrent taken from the generator, means for energizing 10 said field bycurrent taken from the battery, and selective means for rendering saidenergizing means successively efiective, said lective means comprising aswitch connecting said shunt field with the generator during the initialexcitation 15 period and movable substantially simultaneously with theclosing of said reversed current cut-out to a position insuringexcitation of said shunt field directly from the battery.

2. In a system of the class described, a battery 20 and generatorconnected for energization of the former upon rotation of the latter, a.reverse current cut-out between the generator and battery, a, shuntfield constituting part of the generator, and meansior preventing areversal in 25 polarity of the generator regardless of the strength ofthe current passing through said reverse current cut-out, said meansincluding a switch movable to connect said shunt field with the batteryside of the reverse current cut-out as 30 soon as the generator voltagehas built up to the normal running value.

3. In a system of the class described, a battery and generator connectedfor energization of the shunt field with the battery independently ofsaid'reverse current cut-out as soon as the said. terminal voltagereaches the normal running value.

CHARLES I. MCNEIL.

